Memory system including a memory device, and methods of operating the memory system and memory device

ABSTRACT

A method is provided for operating a memory device. The method includes counting, from among memory cells, a number of first off-cells with respect to a first reading voltage and a number of second off-cells with respect to a second reading voltage, comparing the number of first off-cells and the number of second off-cells, and determining, based on a result of the comparing, whether a programming error exists in a storage region in which the memory cells are included.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. patent application Ser. No. 15/639,234,filed Jun. 30, 2017, which is a Divisional of U.S. patent applicationSer. No. 14/456,572, filed Aug. 11, 2014, in which a claim for priorityunder 35 U.S.C. § 119 is made to Korean Patent Application No.10-2013-0096894, filed on Aug. 14, 2013, in the Korean IntellectualProperty Office, the entire contents of which are hereby incorporated byreference.

BACKGROUND

Embodiments of the inventive concept relate to methods of operating amemory device and methods of operating a memory system, and moreparticularly, to methods of operating a memory device whereby aprogramming error of the memory device may be detected, and methods ofoperating a memory system using the method of operating the memorydevice.

Generally, it is desirable for a memory device to provide reliablestorage of data. To this end, after writing data to a memory cell, itmay be determined whether the data has been accurately written. Also,when reading data, an error correction method, such as an error checkand correction (ECC), may be performed to correct data including anerror.

SUMMARY

Embodiments of the inventive concept provide a memory device and methodsof operating a memory device including determining whether programmingof a memory cell in the memory device is performed normally, and amemory system and methods of operating a memory system in order toenable the memory device to stably operate.

According to an aspect of the inventive concept, there is provided amethod of operating a memory device. The method includes counting, fromamong memory cells, a number of first off-cells with respect to a firstreading voltage and a number of second off-cells with respect to asecond reading voltage; comparing the number of first off-cells and thenumber of second off-cells; and determining, based on a result of thecomparing, whether a programming error exists in a storage region inwhich the memory cells are included.

A voltage level of the first reading voltage may be higher than avoltage level of the second reading voltage.

The first reading voltage may correspond to a highest state from amongmultiple states in which the memory cells are programmed. The secondreading voltage may correspond to a second highest state from among thestates in which the memory cells are programmed.

The first reading voltage and the second reading voltage mayrespectively correspond to a first state and a second state from amongmultiple states in which the memory cells are programmed. The firststate may be a state in which a memory cell is programmed last, and thesecond state may be a state to which a memory cell is programmed beforethe first state.

The method may further include reprogramming the memory cells when it isdetermined that a programming error exists.

Comparing the numbers of first and second off-cells may includecalculating a ratio of the number of second off-cells with respect tothe second reading voltage to the number of first off-cells with respectto the first reading voltage.

Comparing the numbers of first and second off-cells may includecalculating numbers of memory cells in which a reading error isgenerated with respect to a first state corresponding to the firstreading voltage and a second state corresponding to the second readingvoltage, respectively; and comparing reading error generation amounts ofthe first state and the second state.

Determining whether a programming error exists may include determiningthat a sudden power-off has occurred during an operation of programmingthe memory cells when the programming error is detected.

The memory cells may include multi-bit memory cells.

According to another aspect of the inventive concept, there is provideda method of operating a memory system. The method includes supplyingpower to a memory device comprising memory cells, detecting whether aprogramming error exists with respect to data programmed in a storageregion of the memory device, and reprogramming the programmed data whena programming error is detected. Detecting whether a programming errorexists is performed based on a result of comparing counted numbers ofmemory cells included in two states from among multiple states in whichthe memory cells are programmed.

The programmed data may be reprogrammed in a region different from thestorage region.

The method may further include treating the storage region as a failregion when programming error is detected in the storage region.

The storage region may be a region which is accessed and programmed lastbefore power to the memory device is interrupted.

The memory device may include a flash memory.

According to another aspect of the inventive concept, there is provideda memory system including a memory device having a memory cell arrayincluding memory cells arranged in storage regions; a memory controllerconfigured to perform control operations with respect to the memorydevice, including programming and reading data; and a programming errordetector configured to determine whether a programming error exists withrespect to a memory cell in a storage region. The programming errordetector includes an off-cell counter, a comparator, and a programmingerror determiner. The off-cell counter is configured to receive firstdata and second data, and to count a number of first off-cells withrespect to a first reading voltage corresponding to a first state and anumber of second off-cells with respect to a second reading voltagecorresponding to a second state, where the first data indicatesrespective states of memory cells read based on the first readingvoltage and the second data indicates respective states of memory cellsread based on the second reading voltage. The comparator is configuredto compare the number of first off-cells and the number of secondoff-cells, or to compare a variation of the number of first off-cellsand a variation of the number of second off-cells, and to determine acomparison result. The programming error determiner is configured todetermine whether the storage region includes a programming error basedon the comparison result.

When the comparator compares the number of first off-cells and thenumber of second off-cells, the comparing may include calculating aratio of the number of second off-cells to the number of first off-cellsto determine the comparison result. The programming error determiner maybe configured to determine that the storage region includes aprogramming error when the comparison result is less than apredetermined determination reference value.

When the comparator compares the variation of the number of firstoff-cells and the variation of the number of second off-cells, thecomparing may include calculating a ratio of the variation of the numberof first off-cells to the variation of the number of second off-cells todetermine the comparison result. The programming error determiner may beconfigured to determine that the storage region includes a programmingerror when the comparison result is greater than a predetermineddetermination reference value.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the inventive concept will be more clearlyunderstood from the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a flowchart illustrating a method of operating a memorydevice, according to an embodiment of the inventive concept;

FIG. 2A is a graph showing a threshold voltage distribution of anormally programmed memory cell;

FIG. 2B is a graph showing a threshold voltage distribution of adeteriorated memory cell;

FIG. 2C is a graph showing a threshold voltage distribution of a memorycell when a sudden power-off state has occurred during a programmingoperation;

FIG. 3 is a schematic block diagram illustrating a memory system,according to an embodiment of the inventive concept;

FIG. 4 is a block diagram illustrating a memory device included in thememory system of FIG. 3, according to an embodiment of the inventiveconcept;

FIGS. 5A and 5B illustrate memory cell arrays included in the memorydevice of FIG. 3, according to embodiments of the inventive concept;

FIG. 6 illustrates examples of memory cells MC1 and MC2 of FIGS. 5A and5B, according to embodiments of the inventive concept;

FIG. 7A is a block diagram illustrating a programming error detectorincluded in the memory system of FIG. 3, according to an embodiment ofthe inventive concept;

FIG. 7B is a block diagram illustrating a programming error detectorincluded in the memory system of FIG. 3, according to another embodimentof the inventive concept;

FIG. 8 is a flowchart illustrating a method of operating the memorydevice of FIG. 1, according to an embodiment of the inventive concept;

FIG. 9 is a flowchart illustrating a method of operating the memorydevice of FIG. 1, according to another embodiment of the inventiveconcept;

FIG. 10 is a flowchart illustrating a method of operating a memorysystem, according to an embodiment of the inventive concept;

FIG. 11 is a block diagram illustrating a memory system, according toanother embodiment of the inventive concept;

FIG. 12 is a block diagram illustrating a memory controller, accordingto an embodiment of the inventive concept;

FIG. 13 is a block diagram illustrating a memory system, according toembodiments of the inventive concept, including a solid state drive(SSD);

FIG. 14 is a block diagram illustrating a server system and a networksystem including the SSD of FIG. 13, according to embodiments of theinventive concept; and

FIG. 15 is a block diagram illustrating a computer device including amemory system, according to embodiments of the inventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments will be described in particular with reference to thefollowing description and accompanying drawings. The inventive concept,however, may be embodied in various different forms, and should not beconstrued as being limited only to the illustrated embodiments. Rather,these embodiments are provided as examples so that this disclosure willbe thorough and complete, and will fully convey the concept of theinventive concept to one of ordinary skill in the art. Accordingly,known processes, elements, and techniques are not described with respectto some of the embodiments. Unless otherwise noted, like referencenumerals denote like elements throughout the attached drawings andwritten description, and thus descriptions may be repeated. In thedrawings, sizes and relative sizes of layers and regions may beexaggerated for clarity.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. Also, the term “exemplary”refers to an example or illustration.

Unless defined differently, terms used in the description includingtechnical and scientific terms have the same meaning as generallyunderstood by those skilled in the art. Terms as defined in a commonlyused dictionary should be construed as having the same meaning as in anassociated technical context, and unless defined apparently in thedescription, the terms are not ideally or excessively construed ashaving formal meaning.

Expressions such as “at least one of,” when preceding a list ofelements, modify the entire list of elements and do not modify theindividual elements of the list.

When a programming operation is performed on a memory cell to store datain a flash memory, for example, each memory cell has a programmingstate. Generally, states of memory cells may indicate predetermined bitsor data, and a threshold voltage distribution of memory cells is formedto correspond to each state. When memory cells are normally programmed,a threshold voltage distribution of the memory cells may have a Gaussiandistribution. However, when a normal programming operation is hindered,for example, by a sudden power-off state that occurs during aprogramming operation, memory cells may not be programmed tocorresponding target states, and an abnormal threshold voltagedistribution of the memory cells may be formed. Accordingly, a readingerror where another state is read instead of a targeted state ofprogramming of multiple memory cells may be generated when readingstates of the memory cells. In addition, a threshold voltagedistribution of the memory cells may deteriorate with time, increasingthe number of memory cells in which reading error is generated.Therefore, whether memory cells that are programmed in a memory deviceare normally programmed is to be checked, and when the memory cells areabnormally programmed, a reprogramming operation is needed to morestably and reliably store data.

A method of operating a memory device, according to an embodiment of theinventive concept, will be described with reference to FIGS. 1 and 2Athrough 2C. FIG. 1 is a flowchart illustrating a method of operating amemory device, according to an embodiment of the inventive concept. FIG.2A is a graph showing a threshold voltage distribution of normallyprogrammed memory cells. FIG. 2B is a graph showing a threshold voltagedistribution of normally programmed, deteriorated memory cells. FIG. 2Cis a graph showing a threshold voltage distribution of abnormallyprogrammed memory cells.

The method of operating a memory device illustrated in FIG. 1 may beperformed in a non-volatile memory device, such as a flash memorydevice, a phase change random access memory (PRAM) using a phase-changematerial, a resistance random access memory (RRAM) using a variableresistance material, such as a transition metal oxide, or a magneticrandom access memory (MRAM) using a ferromagnetic material, for example.Hereinafter, it will be assumed for purposes of illustration that themethod is performed in a flash memory device, including multi-levelcells that store data of at least two bits in each memory cell. Adetailed structure of an illustrative memory cell array included in aflash memory device and of an illustrative structure of a memory cellare described later with reference to FIG. 5A, FIG. 5B and FIG. 6. Ofcourse, other types of memory devices may be incorporated withoutdeparting from the scope of the present teachings.

Referring to FIG. 1, the method of operating a memory device accordingto an embodiment of the inventive concept includes counting, from amongmemory cells in a storage region, the number of off-cells with respectto a first reading voltage and the number of off-cells with respect to asecond reading voltage (S110). The method further includes comparing thenumber of off-cells at the first reading voltage and the number ofoff-cells at the second reading voltage (S120), and determining, basedon a result of the comparing, whether a programming error exists in thestorage region in which the memory cells are included (S130), e.g.,depending on whether a programming operation with respect to the storagearea is performed normally or abnormally. In particular, the method ofoperating the memory device according to the depicted embodimentparticularly relates to a method of detecting a programming error whenprogramming with respect to memory cells is performed abnormally. Thenumber of off-cells with respect to a reading voltage refers to thenumber of memory cells with a threshold voltage higher than the readingvoltage.

Referring to FIG. 2A, the threshold voltage distribution of normallyprogrammed memory cells is shown. In FIG. 2B, the threshold voltagedistribution of the normally programmed, deteriorated memory cellsexhibits different aspects from the threshold voltage distributiondepicted in FIG. 2A. In FIG. 2C, the threshold voltage distribution ofthe abnormally programmed memory cells is significantly different fromthe threshold voltage distributions of both the normally programmedmemory cells (FIG. 2A) and the normally programmed memory cells thatsubsequently deteriorate (FIG. 2B).

First, referring to FIGS. 2A through 2C, a memory cell may be programmedto one of multiple states. For example, when a memory cell is a 2-bitmulti-level memory cell, the memory cell may be programmed to one ofstates E, P1, P2 and P3, as illustrated in FIGS. 2A through 2C. Eachstate indicates a logic value of data stored in the memory cell. Forexample, state E may indicate logic data “11”, state P1 may indicatelogic data “10,” state P2 may indicate logic data “00,” and state P3 mayindicate logic data “01.” The states of the memory cell may beclassified according to reading voltages VRD1, VRD2, and VRD3. Forexample, a memory cell may be read in state P3 when the thresholdvoltage of the memory cell is equal to or greater than the readingvoltage VRD3, may be read in state P2 when the threshold voltage of thememory cell is less than the reading voltage VRD3 and equal to orgreater than the reading voltage VRD2, may be read in state P1 when thethreshold voltage of the memory cell is less than the reading voltageVRD2 and equal to or greater than the reading voltage VRD1, or may beread as state E when the threshold voltage of the memory cell is lowerthan the reading voltage VRD1.

Meanwhile, an off-cell with respect to a reading voltage refers to amemory cell having a threshold voltage that is equal to or greater thanthe particular reading voltage. For example, in FIG. 2A, an off-cellwith respect to the reading voltage VRD3 is in state P3, and an off-cellwith respect to the reading voltage VRD2 is in state P2 or state P3.Likewise, an off-cell with respect to the reading voltage VRD1 is instate P1, P2, or P3. When a threshold voltage of a memory cell decreasesand becomes lower than a reading voltage corresponding to the state towhich the memory cell is programmed, the number of off-cells withrespect to the reading voltage may decrease. In this case, a readingerror occurs when a reading operation is conducted.

Referring further to FIG. 2A, when memory cells are normally programmed,the threshold voltage distribution thereof forms a Gaussian curve foreach state (states E, P1, P2, and P3). Also, each state may beclassified as multiple reading voltages VRD1, VRD2, and VRD3.

When memory cells deteriorate after being normally programmed, the widthof the threshold voltage distribution of the memory cells increases ineach state, as shown in FIG. 2B, for example. Accordingly, although thethreshold voltages of some memory cells of in certain states becomeslower than the corresponding reading voltage VRD1, VRD2, or VRD3, thethreshold voltage distributions of the respective states still form aGaussian distribution, and widths of the threshold voltage distributionsof the states are similar.

However, the threshold voltage distribution of memory cells that areabnormally programmed is different from that of normally programmedmemory cells or memory cells that deteriorate after being programmednormally. When memory cells are abnormally programmed, the width of thethreshold voltage distribution of memory cells in a predetermined stateof the multiple states may be significantly greater than the widths ofthe threshold voltage distributions in other states, as shown in FIG.2C, for example. Referring to FIG. 2C, the threshold voltagedistribution of states E, P1, and P2 is similar to that of normallyprogrammed memory cells, but the width of the threshold voltagedistribution of state P3 is greater than that of the threshold voltagedistribution of the normally programmed memory cell in state P3. Thus,the width of the threshold voltage distribution of state P3 is greaterthan that of the threshold voltage distribution of states E, P1, and P2.This is because programming in state P3 has not been normally performeddue to some unexpected occurrence, such as a sudden power-off, forexample. Generally speaking, when programming is performed abnormally,the threshold voltage distribution of memory cells that are programmedin a predetermined state, from among multiple states in which memorycells may be programmed, may be poorer than that of other memory cellsprogrammed in different states from this predetermined state.

Accordingly, a variation in a reduction of off-cells (hereinafterreferred to as a variation or reduction in the number of off-cells) maybe calculated by counting the number of off-cells with respect to eachof the reading voltages and comparing the counted number of off-cells toa predicted value of the number of off-cells with respect to the readingvoltages, respectively. A reduction in the number of off-cells withrespect to a predetermined voltage may be significantly greater thanthat of the number of off-cells with respect to other thresholdvoltages. The predicted value of the number of off-cells with respect tothe reading voltages is calculated based on the number of programmingstates with respect to the number of memory cells or stored informationof the number of memory cells programmed to respective states whenprogramming is performed to the memory cells.

Referring to FIGS. 2A and 2B, distribution characteristics of therespective states are similar. It may therefore be estimated that thereis not a significant difference between a reduction in the number ofoff-cells with respect to the reading voltage VRD3 and a reduction inthe number of off-cells with respect to the reading voltages VRD2 andVRD1, respectively. However, referring to FIG. 2C, it may be estimatedthat a reduction in the number of off-cells with respect to the readingvoltage VRD3 is significantly different from a reduction in the numberof off-cells with respect to the reading voltage VRD2, for example.

As described above, when a memory cell is abnormally programmed, ascompared to the case of a memory cell being normally programmed, areduction in the number of off-cells with respect to a predeterminedreading voltage is greater than that of the number of off-cells withrespect to other threshold voltages. Thus, whether programming has beenabnormally conducted, that is, whether a programming error exists, maybe detected by counting the number of off-cells with respect tothreshold voltages (reflecting the above characteristics) and comparingthe numbers.

A method of detecting a programming error, according to the currentembodiment, will be described in more detail with reference to FIG. 1and FIGS. 2A through 2C.

First, in operation S110, the number of off-cells with respect to afirst reading voltage and a second reading voltage, respectively, arecounted from among memory cells. The first reading voltage and thesecond reading voltage are voltages among a plurality of voltages usedin reading programmed memory cells. For example, the first readingvoltage may have the highest voltage level (e.g., VRD3), and the secondreading voltage may have a lower voltage level than the first readingvoltage (e.g., VRD2, VRD1) and possibly other reading voltages.Off-cells with respect to the first reading voltage may refer to memorycells having threshold voltages higher than the first reading voltage,and off-cells with respect to the second reading voltage may refer tomemory cells having threshold voltages higher than the second readingvoltage. The first reading voltage may be a reading voltagecorresponding to a first state from among states in which memory cellsare programmed, and the second reading voltage may be a reading voltagecorresponding to a second state. For example, the first state may be thelast state in which a memory cell is programmed, and the second statemay be the state programmed before the first state. When programming amemory cell by increasing a threshold voltage of the memory cell in astepwise manner, the first state may be a state in which the thresholdvoltage of a memory cell is the highest, that is, the highest state, andthe second state may be a state in which the threshold voltage of amemory cell is second to the highest state, that is, the second higheststate. However, the first and second states described herein areexemplary and are not limited thereto. The first and second states maybe determined in various manners, for example, in an order according towhich respective states are programmed or according to types of memorycells. The relationship between the first reading voltage and the secondreading voltage may also vary accordingly.

For example, referring to FIGS. 2A through 2C, the first reading voltagemay be the reading voltage VRD3, and the second reading voltage may bethe reading voltage VRD2. Thus, the first state corresponding to thefirst reading voltage is state P3, and the second state corresponding tothe second reading voltage is state P2. Off-cells with respect to thefirst reading voltage may refer to memory cells in state P3, which havethreshold voltages equal to or greater than the reading voltage VRD3(the first reading voltage), and off-cells with respect to the secondreading voltage may refer to memory cells in state P3 and state P2,which have threshold voltages equal to or greater than the readingvoltage VRD2 (the second reading voltage).

Next, in operation S120, the number of off-cells with respect to thefirst reading voltage (hereinafter referred to as the first off-cellnumber) and the number of off-cells with respect to the second readingvoltage (hereinafter referred to as the second off-cell number) arecompared. The first off-cell number and the second off-cell number maybe compared directly. Alternatively, the number of memory cells in whicha reading error is generated may be calculated with respect to the firstand second states based on the first and second off-cell numbers, andthen the number of memory cells in which a reading error is generatedmay be compared. The number of memory cells in which a reading error isgenerated with respect to the first state refers to the number of memorycells that are programmed in the first state, but are not read as beingin the first state. The number of memory cells including a reading errormay be calculated by counting the number of off-cells and calculatingbased on the counted number, without checking a reading error of each ofthe memory cells through an error check. The number of memory cells inwhich a reading error is generated with respect to respective states mayhave the same meaning as a variation in the number of off-cells.

Referring to FIG. 2B, a memory cell in which a reading error isgenerated with respect to the first state, for example, state P3, andthe second state, for example state P2, is a memory cell in section cand a memory cell in section b. As the numbers of memory cells aresimilar, reading error generation amounts of the first and second statesare similar. Accordingly, the number of off-cells with respect to thefirst reading voltage, for example, the voltage VRD3 (the number ofmemory cells in state P3), and the number of off-cells with respect tothe second reading voltage, for example, the voltage VRD2 (the numbersof memory cells in states P2 and P3), are respectively smaller thanpredicted numbers of memory cells, and reductions in the numbers may besimilar.

However, referring to FIG. 2C, a memory cell in which a reading error isgenerated is only a memory cell in section d that is programmed in stateP3 as a target. Thus, when counting the number of memory cells in stateP3 and counting the numbers of memory cells in states P2 and P3, andcomparing the numbers with a predicted number of memory cells, thereduction in the number of memory cells in state P3 is relatively large,while the reduction in the numbers of memory cells in states P2 and P3may be zero or relatively small.

As described above, the number of off-cells with respect to the firstreading voltage and the number of off-cells with respect to the secondreading voltage are compared in operation S120, and programming errorregarding the storage region in which the memory cells are included isdetermined in operation S130 based on the comparison. As describedabove, when programming is not normally conducted, that is, when aprogramming error has occurred, the reduction in the number of off-cellswith respect to a predetermined reading voltage is greater than thereduction in the number of off-cells with respect to other readingvoltages. Accordingly, an occurrence of a programming error may bedetermined by comparing the number of off-cells with respect to thefirst reading voltage and the number of off-cells with respect to thesecond reading voltage.

Meanwhile, when the number of memory cells including a reading error inthe first and second states is calculated based on the first and secondnumbers of off-cells, and the calculated numbers of memory cellsincluding a reading error are compared, and when reading errorgeneration amounts between the first and second states differ greatly,it may be determined that memory cells have been abnormally programmed.But when the difference between reading error generation is small, itmay be determined that the memory cells have been normally programmed.For example, in an embodiment, when a ratio of generated reading errorsbetween the first and second states calculated in operation S120 isgreater than a predetermined reference value, it may be determined thatmemory cells are abnormally programmed, and when the ratio is smallerthan the predetermined reference value, it may be determined that memorycells are normally programmed. The reference value may be preset, forexample, based on the capacity of the memory cells to be compared.

Referring again to FIG. 2C, the reading error generation amount in stateP3 is significantly greater than that of state P2. Thus, it may bedetermined that memory cells are abnormally programmed using the methodof detecting programming errors according to the current embodiment ofthe inventive concept. However, referring to FIG. 2A, no reading erroris generated, and referring to FIG. 2B, reading error generation amountsof states P3 and P2 are similar. Accordingly, it may be determined thatmemory cells are normally programmed. Accordingly, as illustrated inFIG. 2C, if a sudden power-off has occurred during programming of thememory cells, it may be determined that a programming error is detected.As illustrated in FIGS. 2A and 2C, if programming is normally performed,it may be determined that no programming error is detected.

As described above, according to the exemplary method of operating amemory device, a programming error may be determined by reflectingcharacteristics of threshold voltage distributions of memory cells thatare not normally programmed, thereby increasing the accuracy ofprogramming error detection. Also, instead of determining, for example,whether or not an error bit has been generated, the number of off-cellsregarding threshold voltages is simply counted and the occurrence of aprogramming error is determined using the counted number. Thus,programming error detection may be simplified and a detection speed maybe increased.

Conventionally, the available level of Error Check and Correction (ECC)is determined. It is then determined that programming has been performedabnormally when the number of generated error bits (e.g., the number offail bits) is greater than the available level of ECC, and thatprogramming has been performed normally when the number of generatederror bits is equal to or less than the available level of ECC. However,the number of generated reading error bits of abnormal programming maybe similar to or equal to or less than the number of generated readingerror bits of normal programming. For example, referring to FIGS. 2B and2C, for memory cells that are normally programmed but deteriorate later,a memory cell in which a reading error occurs corresponds to memorycells included in sections a, b, and c of FIG. 2B, and form memory cellsthat are abnormally programmed, a memory cell in which a reading erroroccurs corresponds to a memory cell included in section d of FIG. 2C.Thus, it may be estimated that the number of memory cells included insections a, b, and c may be similar to or greater than the number ofmemory cells included in section d. Accordingly, the number of generatedreading error bits may be greater in FIG. 2B than in FIG. 2C. Ifoccurrences programming errors are determined based on the absolutenumber of generated reading error bits simply with respect to theavailable level of ECC, as is done conventionally, memory cells that arenormally programmed and deteriorate later and memory cells that areabnormally programmed may not be distinguishable from each other.

However, according to the method of determining a programming error ofthe present embodiment, whether a programming error has occurred isdetermined based on relativity of distribution characteristics of apredetermined state to distribution characteristics of other states.Thus, memory cells that are normally programmed and deteriorate laterand memory cells that are abnormally programmed may be distinguishablefrom each other, and a programming error of the memory cells may bedetermined accurately.

FIG. 3 is a schematic block diagram illustrating a memory system 100,according to an embodiment of the inventive concept.

Referring to FIG. 3, the memory system 100 includes a memory device 10and a memory controller 20. The memory controller 20 is configured toperform control operations with respect to the memory device 10. Moreparticularly, the memory controller 20 may control programming(writing), reading, and erasing of data DATA with respect to the memorydevice 10 by providing the memory device 10 with an address ADDR, acommand CMD, and a control signal CTRL.

In the depicted embodiment, the memory device 10 includes a memory cellarray 11. The memory cell array 11 includes memory cells that arearranged in regions where a plurality of word lines and a plurality ofbit lines intersect, respectively. According to various embodiments, thememory cells may be flash memory cells, and the memory cell array 11 maybe a NAND flash memory cell array or a NOR flash memory cell array, forexample. For purposes of illustration, embodiments of the inventiveconcept will be described hereinafter under the assumption that thememory cells are flash memory cells. However, the embodiments are notlimited thereto, and the memory cells may be various other types ofmemory cells, such as resistive memory cells, including resistance RAM(RRAM), phase change RAM (PRAM) or magnetic RAM (MRAM) memory cells, forexample.

When an unexpected event, such as sudden power-off state or a drop inprogramming voltage, occurs while programming memory cells included in aselected word line in the memory cell array 11 of the memory device 10,the programming operation may not be performed normally. Thus, when thememory device 10 returns to a normal state, it must be determinedwhether programming operations with respect to memory cells respectivelyprogrammed before and after occurrence of the unexpected event have beenabnormally performed. That is, it must be detected whether a programmingerror exists. When a programming error is detected, a compensationoperation is additionally performed. To this end, the memory controller20 includes a programming error detector PED.

The memory controller 20 provides the memory device 10 with addresses ofmemory cells that are programmed last (after the memory device 10returns to a normal state), and the memory device 10 may read data DATAfrom memory cells corresponding to the addresses and provide the data tothe memory controller 20. The programming error detector PED may thendetermine whether there is an error in the programming operation of thememory cells based on the data DATA.

The programming error detector PED may operate according to the methodof operating a memory device described with reference to FIG. 1, forexample (he method of detecting a programming error). When theprogramming error detector PED determines that programming has beenperformed abnormally, that is, when it determines that an error in theprogramming operation has occurred, the memory controller 20 may treatan area of memory cells where abnormal programming is performed as a badregion, and provide the memory device 10 with a control signal CTRL or acommand CMD that allows execution of a compensation operation, such asreprogramming data to the memory cells of another region.

FIG. 4 is a block diagram illustrating a memory device 10 included inthe memory system 100 of FIG. 3, according to an embodiment of theinventive concept.

Referring to FIG. 4, the memory device 10 may be a flash memory device,as mentioned above, including memory cell array 11, a row decoder 12, aninput/output (I/O) circuit 13, a voltage generator 14, and control logic15.

The memory cell array 11 includes a plurality of memory cells that arerespectively connected to a plurality of word lines WL and a pluralityof bit lines BL. As described below with reference to FIGS. 5A and 5B,the memory cells may be NAND flash memory cells arranged in atwo-dimensional array structure or a three-dimensional vertical arraystructure. The memory cells may be multi-level cells and may beprogrammed using various programming methods, such as a shadowprogramming method, a reprogramming method, or an on-chip bufferprogramming method, for example.

The row decoder 12 selects memory cells connected to a selected wordline using a method of selecting a word line based on row address XADD.For example, a programming voltage and a verification voltage may beapplied to the selected word line in a write mode, and a reading voltagemay be applied to the selected word line in a read mode, and an erasevoltage may be applied to the selected word line in an erase mode. Avoltage VWL applied to the word line is supplied by the voltagegenerator 14 in response to on voltage control signal VCTRL provided bythe control logic 15.

The input/output circuit 13 is connected to a plurality of bit lines BL,and stores write data to be programmed in the memory cell array 11, orstores read data sensed from the memory cell array 11. The input/outputcircuit 13 may include a plurality of page buffers PB corresponding tothe plurality of bit lines BL, and a column decoder that selects a bitline based on column address YADD. Each of the page buffers PB mayrespectively include a data latch and operate as a write driver or asense amplifier, according to the operational mode of the memory device10. The input/output circuit 13 may load write data provided from theoutside during a programming operation of the write mode, apply aprogramming enable voltage or a programming prohibition voltage to a bitline according to the write data, and may sense a voltage of each bitline in a read mode to output read data.

The control logic 15 generates various control signals to controloverall operation of the memory device 11, and generates a voltagecontrol signal VCTRL, in particular, to control an operation of thevoltage generator 14. According to embodiments of the inventive concept,the control logic 15 may be located inside or outside the memory device11.

The voltage generator 14 generates a word line voltage VWL and a bitline voltage VBL in response to the voltage control signal VCTRL. Theword line voltage VWL provided to the row decoder 12 may include aprogramming voltage, a reading voltage, an erase voltage or the like,according to the corresponding operational mode. The bit line voltageVBL provided to the input/output circuit 13 may include a programmingenable voltage, a programming prohibit voltage, a precharge voltage, orthe like.

FIGS. 5A and 5B are circuit diagrams illustrating memory cell arrays 11a and 11 b included in the memory device 10 of FIG. 2, according toembodiments of the inventive concept.

Referring to FIG. 5A, the memory cell array 11 a includes a plurality ofbit lines BL(1) through BL(m), a plurality of word lines WL(1) throughWL(n), and a plurality of memory cells MC1 arranged in regions where thebit lines BL(1) through BL(m) and the word lines WL(1) through WL(n)intersect. Also, the memory cell array 11 a includes a string selecttransistors SST and ground select transistors GST. The string selecttransistors SST may be connected to the bit lines BL(1) through BL(m),and the ground select transistors GST may be connected to a commonsource line CSL. The memory cells MC1 arranged in the same row may beserially arranged between one of the bit lines BL(1) through BL(m) andthe common source line CSL, and the memory cells MC1 may be commonlyconnected to one of the word lines WL(1) through WL(n). That is, thememory cells MC1 may be serially connected between the string selecttransistors SST and the ground select transistors GST, and multiple(e.g., sixteen, thirty-two or sixty-four) word lines may be arrangedbetween the string select transistors SST and the ground selecttransistors GST.

The string select transistors SST may be connected to a string selectline SSL to be controlled according to a level of a voltage appliedthrough the string select line SSL, and the ground select transistorsSST may be connected to a ground select line GSL to be controlledaccording to a level of a voltage applied through the ground select lineGSL. The memory cells MC1 may be controlled according to a level of avoltage applied to the word lines WL(1) through WL(n) to which they arerespectively connected. The memory cells MC1 respectively connected tothe word lines WL(1) through WL(n) may store data corresponding to apage or multiple pages.

A NAND flash memory device may perform a writing operation (or aprogramming operation) and a reading operation in units of pages PG, andmay perform an erase operation in units of blocks BLK. Informationrelated to a programming operation or an erase operation with respect toeach page is stored in a memory cell allocated to a spare region (or aportion of a main region). This information is referred to as flaginformation FL, and a memory cell that stores flag information isreferred to as a flag cell MF.

For a multi-level cell in which N-bit data is stored per cell, aprogramming operation for each bit may be independently performed up toN times. Also, each programming operation may include multipleprogramming loops. A programming operation with respect to each bit of amulti-level cell (for example, a least significant bit LSB or a mostsignificant bit MSB) may be performed in cells that are connected to thesame word line among the word lines WL(1) through WL(n) in units ofpages. A page address allocated during a programming operation may beallocated continuously toward a word line or discontinuously. A pageaddress that is internally allocated may be internally determined inconsideration of the number of times that a selected memory cell isused.

Referring to FIG. 5B, the memory cell array 11 b includes a plurality ofstrings STR having a vertical structure. The strings STR may be arrangedalong a second direction to form a string row, and a plurality of stringrows may be arranged along a third direction to form a string array. Thestrings STR may each include ground select transistors GSTV that areserially arranged in a first direction between the bit lines BL(1)through BL(m) and the common source line CSL, memory cells MC2, and astring select transistor SSTV.

The ground select transistors GSTV may be respectively connected to aplurality of ground select lines GSL11, GSL12, . . . , GSLi1, GSLi2, andthe string select transistors SSTV may be respectively connected to aplurality of string select lines SSL11, SSL12, . . . , SSLi1, SSLi2. Thememory cells MC2 arranged in the same layer may be commonly connected toone of the word lines WL(1) through WL(n). The ground select linesGSL11, . . . , GSLi2 and the string select lines SSL11, . . . , SSLi2may extend in the second direction and may be arranged in the thirddirection. The word lines WL(1) through WL(n) may extend in the seconddirection, and may be arranged in the first direction and the thirddirection. The bit lines BL(1) through BL(m) may extend in the thirddirection and may be arranged in the second direction. The memory cellsMC2 may be controlled according to a level of a voltage applied to theword lines WL(1) through WL(n).

A vertical type flash memory device including the memory cell array 11 bincludes NAND flash memory cells. Thus, the vertical type flash memorydevice also performs a writing operation and a reading operation inunits of pages, and performs an erase operation in units of blocks, likea typical NAND flash memory device.

According to embodiments of the inventive concept, two string selecttransistors included in a string STR may be connected to a string selectline, and two ground select transistors included in a string STR may beconnected to a ground select line. Also, according to embodiments of theinventive concept, a string may include a string select transistor and aground select transistor.

FIG. 6 illustrates examples of memory cells MC1 and MC2 of FIGS. 5A and5B, according to embodiments of the inventive concept.

Referring to FIG. 6, a source S and a drain D are formed on a substrateSUB, and a channel region is formed between the source S and the drainD. A floating gate FG is formed on the channel region, and an insulatinglayer, such as a tunneling insulating layer, may be disposed between thechannel region and the floating gate FG. A control gate CG is formed onthe floating gate FG, and an insulating layer, such as a blockinginsulating layer, may be disposed between the floating gate FG and thecontrol gate CG. Voltages needed for programming, reading or erasingwith respect to the memory cells MCEL may be applied to the substrateSUB, the source S, the drain D, and the control gate CG.

Regarding the flash memory device, data stored in a memory cell MCEL maybe read by distinguishing a threshold voltage Vth of the memory cellMCEL. The threshold voltage Vth of the memory cell MCEL may bedetermined according to the amount of electrons stored in the floatinggate FG. In particular, as more electrons are stored in the floatinggate FG, the threshold voltage of the memory cell MCEL becomes higher.

Electrons stored in the floating gate FG of the memory cell MCEL mayleak in the direction indicated by arrows due to various reasons, andaccordingly the threshold voltage of the memory cell MCEL changes isresponse. For example, electrons stored in the floating gate FG may leakdue to abrasion of the memory cell MCEL. In particular, an insulatinglayer between the channel region and the floating gate FG may be wornaway when access operations, such as programming, reading and/or erasingwith respect to the memory cell MCEL are repeated, causing electronsstored in the floating gate FG to leak. Also, electrons stored in thefloating gate FG may leak due to high-temperature stress or atemperature difference between programming and reading operations. Suchleakage may deteriorate the memory device.

Meanwhile, when a programming operation is abnormally performed,electrons stored in the floating gate FG may be less than when aprogramming operation is normally performed. Accordingly, the thresholdvoltage of the memory cell MCEL may decrease, and the number ofelectrons stored in the floating gate FG that are leaked may increasewith time.

FIG. 7A is a block diagram illustrating a programming error detector ofthe memory system of FIG. 3, according to an embodiment of the inventiveconcept. FIG. 7B is a block diagram illustrating a programming errordetector of the memory system of FIG. 3, according to another embodimentof the inventive concept.

Referring to FIG. 7A, a programming error detector PED includes anoff-cell counter CNT, a comparator CMP, and a programming errordeterminer DET.

The off-cell counter CNT receives first data DATA1 and second dataDATA2, and counts the number of off-cells with respect to a firstreading voltage and the number of off-cells with respect to a secondreading voltage. The first data DATA1 indicates respective states ofmemory cells read based on the first reading voltage corresponding to afirst state, and the second data DATA2 indicates respective states ofmemory cells read based on the second reading voltage corresponding to asecond state. For example, when the first state is state P3 of FIG. 2C,and the second state is state P2 of FIG. 2C, the first data DATA1 may bestate information of each of memory cells that are read by reading thememory cells based on a reading voltage VRD3, and the second data DATA2may be state information of each of memory cells that are read byreading the memory cells based on a reading voltage VRD2. A logic value“1” in the first data DATA1 indicates that a corresponding memory cellis an off-cell with respect to the reading voltage VRD3 (hereinafterreferred to as first off-cell), and a logic value “1” in the second dataDATA2 indicates that a corresponding memory cell is an off-cell withrespect to the reading voltage VRD2 (hereinafter referred to as secondoff-cell). The off-cell counter CNT may count the number of firstoff-cells, that is, the number of memory cells read as being in thefirst state, by counting the number of logic value “1” of the first dataDATA1. The counted number may be output as the number of first off-cellsOFF1. In addition, by counting the number of logic value “1” of thesecond data DATA2, the number of the second off-cells, that is, thenumber of memory cells that are read as being in the first state or thesecond state, may be counted. The counted number of the second off-cellsmay be output as the number of second off-cells OFF2.

The comparator CMP compares the number of first off-cells OFF1 and thenumber of second off-cells OFF2, and outputs a comparison result RCMP. Aratio of the number of second off-cells OFF2 to the number of firstoff-cells OFF1 may be output as the comparison result RCMP.Alternatively, variations of the number of first off-cells OFF1 and thenumber of second off-cells OFF2 may be calculated, and a ratio betweenthese variations may be output as the comparison result RCMP. Inaddition, other various comparison methods may be used.

The programming error determiner DET determines whether a storage regionincluding memory cells includes a programming error based on thecomparison result RCMP. The programming error determiner DET maydetermine that a programming error is present when the comparison resultRCMP is either greater or less than a predetermined determinationreference value. For example, when the comparison result RCMP regardinga reading error includes the ratio of the number of second off-cellsOFF2 to the number of first off-cells OFF1, and the comparison resultRCMP is smaller than a predetermined determination reference value, itmay be determined that a programming error exists. Alternatively, whenthe comparison result RCMP regarding a reading error includes a ratio ofa variation in the number of second off-cells OFF2 with respect to avariation in the number of first off-cells OFF1, and the comparisonresult RCMP is greater than a predetermined determination referencevalue, it may be determined that a programming error exists. That is,when it is determined that programming is abnormally performed, it maybe estimated that a condition, such as a sudden power-off state, hasoccurred during programming of one or more memory cells.

Referring to FIG. 7B, the programming error detector PED includes anoff-cell counter CNT, an error cell calculator CAU, a comparator CMP,and a programming error determiner DET. Compared to FIG. 7A, theprogramming error detector PED includes the error cell calculator CAU asan additional component.

The error cell calculator CAU calculates the number ER1 of first errorcells with respect to the first state, and the number ER2 of seconderror cells with respect to the second state based on the number offirst off-cells OFF1 and the number of second off-cells OFF2,respectively, provided by the off-cell counter CNT.

The comparator CMP compares the number ER1 of first error cells withrespect to the first state (first error cell number ER1) and the numberER2 of second error cells with respect to the second state (second errorcell number ER2). The number of error cells is the same as a variationin the numbers of off-cells, and thus, comparing the numbers of errorcells may be the same as comparing the number of off-cells.

Based on the comparison result RCMP, the programming error detector PEDdetermines whether a storage region including memory cells includes aprogramming error. The programming error determiner DET may determinethat a programming error is present when the comparison result RCMP isgreater than a predetermined determination reference value, for example.

FIG. 8 is a flowchart illustrating operation a memory device accordingto the flowchart of FIG. 1, according to an embodiment of the inventiveconcept. The flowchart of FIG. 8 shows each operation of the methoddepicted in FIG. 1 in more detail.

Referring to FIG. 8, the number of first off-cells OFF1 is counted inoperation S111, and the number of second off-cells OFF2 is counted inoperation S112. As described above, the first off-cells are off-cellswith respect to a first reading voltage, and the second off-cells areoff-cells with respect to a second reading voltage. When a level of thefirst reading voltage is higher than that of the second reading voltage,the first off-cells are memory cells in the first state, and the secondoff-cells are memory cells in the first or second states.

As described above with reference to FIG. 7A, the number of firstoff-cells OFF1 may be counted based on data obtained by reading statesof memory cells with respect to the first reading voltage (DATA1 of FIG.7A). Also, the number of second off-cells OFF2 may be counted based ondata obtained by reading states of memory cells with respect to a secondreading voltage (DATA2).

In operation S120 a, the number of first off-cells OFF1 and the numberof second off-cells OFF2 are compared. According to the depictedembodiment, the comparison result RCMP is calculated as a ratio of thenumber of first off-cells OFF1 with respect to the number of secondoff-cells OFF2 (OFF1/OFF2).

Then, in operation S130 a, whether there is a programming error isdetermined based on the comparison result RCMP. According to thedepicted embodiment, the comparison result RCMP is compared to apredetermined reference value PREF1 (hereinafter referred to as firstdetermination reference value) in operation S131 a. When the comparisonresult RCMP is less than the first determination reference value PREF1,it is determined in operation S132 that a programming error exists(programming is abnormal). When the comparison result RCMP is greaterthan or equal to the first determination reference value PREF1, it isdetermined in operation S133 that programming is normal. The firstdetermination reference value PREF1 may be set in consideration of acapacity of a memory cell to be programmed, a threshold voltagedistribution of a programming state, a voltage level of a readingvoltage, or a calculation method, for example.

FIG. 9 is a flowchart illustrating operation of a memory deviceaccording to the flowchart of FIG. 1, according to another embodiment ofthe inventive concept. The flowchart of FIG. 9 shows each operation ofthe method depicted in FIG. 1 in more detail.

Referring to FIG. 9, the number of first off-cells OFF1 is counted inoperation S111, and the number of second off-cells OFF2 is counted inoperation S112, which is the same as in FIG. 8. Thus, the descriptionwill not be repeated.

After the number of first off-cells OFF1 and the number of secondoff-cells OFF2 are counted in operation S110 a, the numbers of firstoff-cells OFF1 and the number of second off-cells OFF2 are compared inoperation S120 b. According to the depicted embodiment, the number offirst off-cells OFF1 and the number of second off-cells OFF2 are notdirectly compared. Rather, first and second error cell numbers ER1 andER2, indicating numbers of first and second error cells with respect tothe first and second states, respectively, are calculated based on thenumber of first off-cells OFF1 and the number of second off-cells OFF2.The first and second error cell numbers ER1 and ER2 are compared.

In particular, the number ER1 of first error cells with respect to thefirst state is calculated in operation S121 by determining thedifference between a first reference value REF1 and the number of firstoff-cells OFF1. The number ER2 of second error cells with respect to thesecond state is calculated in operation S122 by determining thedifference between a second reference value REF2 and the number ofsecond off-cells OFF2. The first reference value REF1 and the secondreference value REF2 may be predicted values with respect to the numberof first off-cells OFF1 and the number of second off-cells OFF2,respectively. That is, the first reference value REF1 and the secondreference value REF2 may be the number of the first off-cells and thenumber of the second off-cells when programming is normally performed.The numbers ER1 and ER2 of first and second error cells with respect tothe first and second states may be the same as variations in the numbersof the first and second off-cells OFF1 and OFF2, respectively.

Next, in operation S123, a ratio between the number ER1 of first errorcells with respect to the first state and the number ER2 of second errorcells with respect to the second state is calculated as comparisonresult RCMP (ER1/ER2).

In operation S130 b, occurrence of a programming error may be determinedby comparing the comparison result RCMP with a predetermined referencevalue PREF2 (hereinafter referred to as second determination referencevalue) in operation S131 a. When the comparison result RCMP is greaterthan the second determination reference value PREF2, it is determined inoperation S132 that a programming error exists (programming isabnormal). When the comparison result RCMP is less than or equal to thesecond determination reference value PREF2, it is determined inoperation S133 that programming is normal. The second determinationreference value PREF2 may be set in consideration of a capacity of amemory cell to be programmed, a threshold voltage distribution of aprogramming state, a voltage level of a reading voltage, or acalculation method, for example.

Illustrative methods of operating a memory device according to theembodiments of the inventive concept are described above with referenceto FIGS. 8 and 9. However, the embodiments are not limited thereto, andother various calculation and/or comparison operations may be usedwithout departing from the scope of the present teachings.

FIG. 10 is a flowchart illustrating a method of operating a memorysystem, according to an embodiment of the inventive concept.

Referring to FIG. 10, power is supplied to the memory device inoperation S1100. An occurrence of a programming error in a storageregion is detected in operation S1200 when the power is supplied. Theprogramming error may be detected by applying a method of detecting aprogramming error described above with reference to FIGS. 1, 8 and 9.For example, occurrence of a programming error may be determined basedon a result of comparing counted numbers of memory cells included in twostates from among multiple states in which the memory cells areprogrammed. The two states may be the highest state and the secondhighest state from among multiple states to which memory cells areprogrammed. Alternatively, the two states may be a state in which amemory cell is programmed last and a state in which a memory cell isprogrammed next to the last state. Also, for example, the storage regionmay be a storage region that is programmed last before power to thememory device is interrupted.

When a programming error is detected, programmed data is reprogrammed inoperation S1300. For example, when a programming error is detected, itmay be determined that a sudden power-off state occurred whileprogramming the storage region that was last programmed. When thestorage region is abnormally programmed, a reading error generationratio is high and deterioration may occur quickly, and thus aprogramming error may be difficult to correct, even using an errorcorrection method, such as ECC. Accordingly, the programmed data isreprogrammed to stably store the data. A storage region where the datais reprogrammed may be different from the storage region that was lastprogrammed. After reprogramming data in operation S1300, the storageregion may be treated as a fail region.

As described above, when a programming error is detected, afterperforming a compensation operation, a typical write/read operation ofdata may be performed in operation S1400.

FIG. 11 is a schematic block diagram illustrating a memory system 100 a,according to another embodiment of the inventive concept.

Referring to FIG. 11, the memory system 100 a includes a memory device10 a and a memory controller 20 a. The memory device 10 a and the memorycontroller 20 a operate in a similar manner as the memory device 10 andthe memory controller 20 described above with reference to FIG. 3. Thedifference is that the programming error detector PED is located in thememory device 10 a of the memory system 100 a (as opposed to the memorycontroller 20). That is, the memory device 10 a may include an on-chipcontroller, enabling the programming error detector PED to be includedin the memory device 10 a.

The programming error detector PED may operate in substantially the samemanner as the programming error detector PED of FIG. 3. When the memorycontroller 20 a provides the memory device 10 a with an address ofmemory cells that are accessed last and programmed, and the memorydevice 10 a reads data DATA from the memory cells corresponding to theaddress, the programming error detector PED receives first data DATA1corresponding to a first state and second data DATA2 corresponding to asecond state, and may detect occurrence of a programming error based onmethods of detecting a programming error described above with referenceto FIGS. 1, 8, and 9. When a programming error is detected, aprogramming error detection signal Dec_err is provided by theprogramming error detector PED to the memory controller 20 a. Inresponse to the programming error detection signal Dec_err, the memorycontroller 20 a may treat the region of a memory cell in whichprogramming is abnormally performed as a bad region, and may transmit acontrol signal CTRL and a command CMD to the memory device 10 to performa compensation operation, such as reprogramming of a memory cell ofanother region.

FIG. 12 is a block diagram illustrating a memory controller, accordingto an embodiment of the inventive concept.

Referring to FIG. 12, memory controller MCtrl includes a host interfaceunit HIF, a memory interface unit MIF, a local memory LMEM, a bufferBUF, a processor PRO, and a programming error detector PEC, which may beconnected via a bus.

The host interface unit HIF provides an interface with respect to anexternal host device HOST. For example, the host interface unit HIF mayoperate according to a variety of interface protocols, such as SerialAdvanced Technology Attachment (SATA) or Serial Attached SCSI (SAS), butis not limited thereto. For example, the host interface unit HIF mayinclude various other interface protocols, such as Universal Serial Bus(USB), Man Machine Communication (MMC), Peripheral ComponentInterconnect-Express (PCI-E), Parallel Advanced Technology Attachment(PATA), Small Computer System Interface (SCSI), Enhanced Small DeviceInterface (ESDI), or Intelligent Drive Electronics (IDE).

The memory interface unit MIF provides an interface with a memory deviceMDEV to program or read data to or from the memory device MDEV inresponse to a request by the host device HOST. For example, the memoryinterface unit MIF may provide a result of converting a logical blockaddress transmitted by the host device HOST to a physical addressregarding a page of the memory device MDEV to the memory device MDEV.

The buffer BUF is used to facilitate data transmission between the hostdevice HOST and the memory device MDEV. For example, the buffer BUF maytemporarily store data to be programmed to the memory device MDEVaccording to a request by the host device HOST. Alternatively, thebuffer BUF may temporarily data that is read from the memory device MDEVaccording to a request by the host device HOST. The buffer BUF may beimplemented by volatile memory, such as dynamic random access memory(RAM) (DRAM) or static RAM (SRAM), or non-volatile memory, such asmagnetic RAM (MRAM), phase-change RAM (PRAM), ferroelectric RAM (FRAM)or flash memory.

Data and a control module or a control program that are used for thememory controller MCtrl to process request of the host device HOST inthe memory device MDEV, may be stored in the local memory LMEM. Forexample, firmware may be stored in the local memory LMEM. Generally,firmware is software in the form of hardware, which includes a commandand data to derive the memory system MSYS in a predetermined storageunit, and perform at least one process, such as machine code processing,regarding a request of a host device, data transmission, listprocessing, floating point operation, or channel control, in order toperform requests by the host device HOST with respect to the memorysystem MSYS. In addition, the local memory LMEM may store, for example,a mapping table that is referred to in an operational system or addressmapping. Like the buffer BUF, the local memory LMEM may be formed ofvolatile memory, such as DRAM or SRAM, or non-volatile memory, such asMRAM, PRAM, FRAM or flash memory. However, a local memory LMEM thatoperates as firmware may be a non-volatile memory. The local memory LMEMmay be at least one of a homogeneous memory or heterogeneous memory.

The processor PRO is configured to control operations of each element ofthe memory controller MCtrl. The processor PRO may interpret or executea control module or a control program that is stored or loaded in thelocal memory LMEM, thereby processing a request from the host deviceHOST.

The programming error detector PED may count the number of off-cellswith respect to a first reading voltage and off-cells with respect to asecond reading voltage based on data read from the memory device MDEV,and may compare the counted numbers values to detect programming errors.When a programming error is detected, it is determined that aprogramming operation performed with respect to memory cells has notbeen normally performed. Accordingly, the memory controller MCtrl maycontrol the memory device MDEV to reprogram the affected data.

When the memory system 100 of FIG. 3 and/or the memory system 100 a ofFIG. 11, according to various embodiments, include a solid state drive(SSD) or are in an SSD, the memory controller MCtrl of FIG. 12 may beincluded in an SSD controller SCtrl of FIG. 13, for example.

FIG. 13 is a block diagram illustrating a memory system, according toembodiments of the inventive concept, applied to an SSD.

Referring to FIG. 13, SSD MSYS includes an SSD controller SCtrl and amemory device MDEV. The SSD controller SCtrl controls the memory deviceMDEV in response to signals SIG received from the host device HOST via afirst port PT1 of the SSD MSYS. The SSD controller SCtrl may beconnected to the memory device MDEV through multiple channels Ch1through Chn. The memory device MDEV may include multiple non-volatilememories NVM1 through NVMn. The non-volatile memories NVM1 through NVMnmay be flash memories MEM, for example, according to embodimentsdescribed above. However, the memory device MDEV is not limited thereto,and may include other flash memories or other non-volatile memories.

The SSD MSYS may further include an auxiliary power supply DSP toreceive power PWR from a host device HOST through a second port PT2.However, embodiments of the inventive concept are not limited thereto,and the SSD MSYS may receive power from an external device other thanthe host device HOST.

The SSD MSYS outputs result of processing requests from of the hostdevice HOST through the first port PT1.

FIG. 14 is a block diagram illustrating a server system SVSYS and anetwork system NSYS including the SSD of FIG. 13, according toembodiments of the inventive concept.

Referring to FIG. 14, the network system NSYS includes the server systemSVSYS and multiple terminals TEM1 through TEMn that are connectedthrough a Network. The server system SVSYS includes a server SERVER thatprocesses requests received through one or more of the terminals TEM1through TEMn connected to the Network and an SSD that stores data DTAcorresponding to the requests received by the terminals TEM1 throughTEMn. The SSD of FIG. 14 may be the SSD of FIG. 13, for example.

FIG. 15 is a block diagram illustrating a computer device including amemory system CSYS, according to the embodiments of the inventiveconcept.

Referring to FIG. 15, the computer system CSYS includes a centralprocessing unit CPU, a user interface UI, and a memory system MSYS thatare electrically connected to a bus. The memory system MSYS may be thememory system 100 of FIG. 3 or the memory system 100 a of FIG. 11, forexample, according to various embodiments. The computer system CSYS mayfurther include a power supply device PS. Also, the computer system CSYSmay further include a volatile memory device (e.g., RAM) for datatransmission and reception between the central processing unit CPU andthe memory system MSYS.

If the computer system CSYS is a mobile device, a battery for supplyingoperational voltage of the computer system CSYS and a modem, such as abaseband chipset, may be also included. In addition, as would beapparent to one of ordinary skill in the art, an application chipset, acamera image processor (CIS), a mobile DRAM, or the like may be furtherincluded in the computer system CSYS of the present embodiment.

While the inventive concept has been described with reference toexemplary embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the inventive concept. Therefore, it shouldbe understood that the above embodiments are not limiting, butillustrative.

What is claimed is:
 1. A method of operating a memory device includingat least one storage region, the storage region including a plurality ofmemory cells, and each of the plurality of memory cells being programmedinto a state among at least four states, the method comprising:counting, among the plurality of memory cells in the storage region, afirst number of off-cells in a first group of memory cells with respectto a first reading voltage and a second number of off-cells in a secondgroup of memory cells with respect to a second reading voltage;comparing the first number with the second number; and determining,based on a result of the comparing, whether a programming error existsin the storage region in which the plurality of memory cells areincluded, wherein the first group of memory cells has been programmedfor a highest state among the at least four states and the second groupof memory cells has been programmed for a second highest state among theat least four states.
 2. The method of claim 1, wherein it is determinedthat the programming error exists when the first number is substantiallygreater than the second number.
 3. The method of claim 1, wherein avoltage level of the first reading voltage is higher than a voltagelevel of the second reading voltage.
 4. The method of claim 1, whereinthe first reading voltage corresponds to a minimum voltage level of thehighest state.
 5. The method of claim 4, wherein the second readingvoltage corresponds to a minimum voltage level of the second higheststate.
 6. The method of claim 1, wherein the second group of memorycells for the second highest state is programmed before programming thefirst group of memory cells for the highest state.
 7. The method ofclaim 1, further comprising a step of reprogramming the plurality ofmemory cells when it is determined that the programming error exists. 8.The method of claim 1, wherein the comparing the first number with thesecond number comprises calculating a ratio of the first number and thesecond number.
 9. The method of claim 1, wherein the programming errorexists when a sudden power-off has occurred during programming theplurality of memory cells.
 10. The method of claim 1, wherein each ofthe plurality of memory cells includes at least two-bit data.
 11. Amethod of operating a memory device including at least one storageregion, the storage region including a plurality of memory cells, andeach of the plurality of memory cells being programmed into a stateamong at least four states, the method comprising: counting, among theplurality of memory cells in the storage region, a first number ofoff-cells in a first group of memory cells with respect to a firstreading voltage and a second number of off-cells in a second group ofmemory cells with respect to a second reading voltage; comparing thefirst number with the second number; and determining, based on a resultof the comparing, whether a programming error exists in the storageregion in which the plurality of memory cells are included, wherein thefirst group of memory cells has been programmed for a first state whichis a highest state among the at least four states and the second groupof memory cells has been programmed for a second state among the atleast four states, and the second state is different from the firststate.
 12. The method of claim 11, wherein it is determined that theprogramming error exists when the first number is greater than thesecond number.
 13. The method of claim 11, wherein a voltage level ofthe first reading voltage is higher than a voltage level of the secondreading voltage.
 14. The method of claim 11, wherein the first readingvoltage corresponds to a minimum voltage level of the first state. 15.The method of claim 14, wherein the second reading voltage correspondsto a minimum voltage level of the second state.
 16. The method of claim11, wherein the second group of memory cells for the second state areprogrammed before programming the first group of memory cells for thefirst state.
 17. The method of claim 11, further comprising a step ofreprogramming the plurality of memory cells when it is determined thatthe programming error exists.
 18. The method of claim 11, wherein thecomparing the first number with the second number comprises calculatinga ratio of the first number and the second number.
 19. The method ofclaim 11, wherein the programming error exists when a sudden power-offhas occurred during programming the plurality of memory cells.
 20. Themethod of claim 11, wherein each of the plurality of memory cellsincludes at least two-bit data.